1. Field
The presently disclosed embodiments relate generally to systems, methods, apparatuses, and computer readable media for position location of wireless mobile devices, and more particularly to such systems, methods, apparatuses, and computer readable media for managing almanac data for use in position location functions by such devices.
2. Background
Mobile communication technologies have recently enjoyed substantial growth which is likely to continue in the future. Currently, many cars, trucks, airplanes, boats, and other vehicles are equipped with devices that allow convenient and reliable mobile communication through a network of satellite-based or land-based transceivers. Advances in this technology have also led to widespread use of hand-held, portable mobile communication devices.
Many customers of mobile communications systems also find an accurate determination of their location to be desirable. To this end, numerous location-based services have emerged. For example, services such as directions or the location of nearby facilities of a desired type may be provided based on the location information developed by the wireless device.
In the past, location information has been principally generated by satellite positioning systems (SPSs), such as the global positioning system (GPS) using NAVSTAR satellites, the Russian GLONASS system, or the European EUTELSAT system, or a land-based positioning system, such as LORAN-C. However, recent demands for faster, more accurate, and more reliable position location determination have been met with additional means to assist in, or supplant entirely, the former SPS techniques. For example, to improve the accuracy of the location information derived SPSs, or the like, fixed base stations at known locations have been used to send assistance data for mobile device use.
The use of assistance information has a number of advantages. Current cellular base stations are positioned in relatively close proximity to mobile devices in which they are in communications, as well as to adjacent or nearby other cellular base stations. The use of assistance data improves or extends the capabilities of satellite positioning systems, enabling operation in places previously not possible, since it improves time-to-fix- and sensitivity. Additionally, improved accuracy may be obtained from having more numerous and closely spaced receivers to account for atmospheric and other effects which tend to degrade the accuracy of positioning systems. Moreover, as additional base stations are deployed in the future, even more densely than current systems, they are likely to continue to provide even better resolution.
Although many of today's wireless communication standards provide for transmission of base station almanac data (BSA), currently deployed wireless base station systems typically do not broadcast their own almanac data. In general, even though the BSA data could be provided, it would not be the most effective or cost efficient technique, because it would be primarily transaction based, requested, for instance, on an ad hoc, or as-needed, basis. That is, each time a mobile device initiated a position location application or service, it would have to request the base station almanac data.
Thus, currently, BSA needs to be obtained from a location server serving the mobile devices; consequently, mobile devices must contact the server for their almanac information. In most cases, the location server does not have any way to contact the mobile devices to keep the BSA up-to-date. Although the server may have downloaded the BSA, for example, two hours ago, the server typically has no memory of that download, and the BSA must be re-downloaded when it is again needed, even if it is the same data that the mobile device already has. This, of course, takes time, bandwidth, and other resources.